1. Technical Field
The present invention relates to a screen, a projection system, a front projection television receiver, and a screen manufacturing method.
2. Related Art
A reflection type screen which reflects projection light received from a projector or the like to show a visually recognizable image on the screen is known. Recently, such a reflection type screen which improves optical characteristics by using a number of micro-lenses (micro-lens array), that is, small semispherical convexes disposed on the reflection surface of the screen for reflecting the projection light has been proposed.
JP-A-2003-195029 proposes a technology which delivers ultraviolet hardening resin to a lyophilic area having a circular pattern, raises compositions of the resin on the lyophilic area by utilizing the wettability difference between the lyophilic area and other area (liquid repellency area), and hardens the raised resin to form semispherical convex micro-lenses.
In addition, JP-A-2006-215162, FIG. 2 discloses a technology which forms the shapes of the micro-lenses by ¼ spherical convexes as halves of the semispherical convexes.
According to the screen which has a number of small convexes or concaves on the reflection surface, the screen gain improves in the area directly receiving the projection light. However, substantially no improvement of the screen gain can be recognized in the area not directly receiving the projection light.
For example, when the projection light is diagonally supplied from below to the screen, an area not receiving the light exists in the upper portion of each lens in case of the micro-lenses having convexes. Also, an area not receiving the light exist in the lower portion of each lens in case of the micro-lenses having concaves. These portions scarcely contribute to the improvement of the screen gain.
Thus, according to the screen which includes the micro-lenses having the semispherical convexes on the reflection surface, the screen gain does not sufficiently increase, and the visibility of the image projected on the screen lowers.
For overcoming these problems, JP-A-2006-215162 proposes the structure which disposes the ¼ spherical convexes adjacent to each other in the incident direction of the projection light. According to this structure, the portion not contributing to the improvement of the screen gain decreases, while the portion contributing to the improvement of the screen gain increases.
In this case, however, the contrast lowers due to the effect of external light coming from a ceiling light or the like.
More specifically, when the projection light is diagonally supplied from below to the screen similarly to the above case, for example, the spherical surface of the ¼ spherical convex on which a reflection film is formed is disposed in the lower region, and the flat surface is disposed in the upper region. In this case, the flat surface not having the reflection film also has the reflection characteristics to some extent depending on the material. Thus, when external light is supplied from the ceiling light or the like to the screen, the external light is reflected by the flat surface. The reflection light then reaches the spherical surface of the convex disposed immediately above and is reflected thereby toward the front. As a result, the contrast lowers, and thus the visibility of the image projected on the screen decreases.